It is creepy to go on about 'Jewish leftists' and 'within the tribe' ('tribe'?). But most clearly Blankfort is wrong when he says that the blame lies primarily with Israel not the US, and Chomsky is right when he says blame lies primarily with the US (and, I would add those other western allies).
Further, Blankfort is tactically wrong about the boycott. Boycotts can work, but have some drawbacks. In the case of Israel, the boycotts (and attacks upon) Jewish owned shops like Marks and Spencers (here in the UK) are grotesque - making the issue into one of attacking Jewish shopkeepers rather than western imperialism.
Chomsky might have been mistaken in the 1950s, about left-wing Zionism (lots were, including my aunt). But his position today seems honourable to me.